A general problem in the telecommunications field is to convey data packets between different devices or parts of a device in an efficient manner. Data switches are an example of a type of device in which this problem can occur. Switches are used to selectively route data signals to their destinations.
A typical switch comprises a number of line cards which each provide an interface to one or more data lines. The data lines typically comprise optical fibers. When a packet is received at a line card, the packet is sent to a fabric interface card that interfaces to a switch fabric. The switch fabric determines an output data line on which the packet should be sent to reach its destination. This determination may be made, for example, on the basis of information in the packet's header. The switch fabric then routes the packet, by way of a fabric interface card, to the line card which is connected to the output data line. An example of a switch which has this general architecture is the ALCATEL™ model 7670 switch.
Communication between the line cards and fabric interface cards is generally provided over a midplane. The midplane is typically limited in terms of the number of signal paths that it can maintain between different cards. Consequently, the midplane can present a bottleneck which interferes with reaching the goal of higher throughput. There is continual pressure to increase the rate at which packets can be handled. Currently it is desired to support the OC-192 standard which operates at 10 Gbps data rates.
Various protocols exist which could be used to provide high speed data communications over a midplane. None of these currently available protocols are ideal. Available protocols include POS-PHY4 (Packet over SONET—Physical Layer 4) and FlexBus4™. A problem with POS-PHY4 is that it is difficult to implement in a cost-effective manner using ASICs (application specific integrated circuits) and FPGAs (field programmable gate arrays). FlexBus4 requires an interface which has an undesirably high pin-count. This increases the cost of providing switch hardware which uses the FlexBus4 protocol to carry data.
Lower-rate interfaces such as Utopia3 (universal test and operations physical interface for ATM) exist. Utopia3 provides a 32 bit bus operating at up to 100 MHz for data rates up to 3.2 Gbs. However, it has so far not been considered to be practical to provide increased bandwidth by using several such interfaces simultaneously because cells can get out of sequence.
There remains a need for cost-effective methods for transmitting data at high speed between devices over a pin-limited interface. There is currently a particular need for such methods capable of handling OC-192 data rates, which require an aggregate bandwidth of at least 12.8 Gps. In the future it will be desirable to accommodate higher data rates.